Radio frames in a Long Term Evolution (LTE) system and an LTE-Advanced (LTE-A) system include frame structures of a Frequency Division Duplexing (FDD) mode and a Time Division Duplexing (TDD) mode. FIG. 1 is a schematic diagram of a frame structure in an existing LTE/LTE-A FDD system. As shown in FIG. 1, one radio frame of 10 milliseconds (ms) is composed of twenty time slots each having a length of 0.5 ms and numbered from 0 to 19. The time slots 2i and 2i+1 constitute a subframe i having a length of 1 ms. FIG. 2 is a schematic diagram of a frame structure in an existing LTE/LTE-A TDD system. As shown in FIG. 2, one radio frame of 10 ms is composed of two half frames each having a length of 5 ms. One half frame includes 5 subframes each having a length of 1 ms. The subframe i is defined as 2 time slots 2i and 2i+1 each having a length of 0.5 ms respectively.
In the two kinds of frame structures above, for a Normal Cyclic Prefix, one time slot contains 7 symbols each having a length of 66.7 microseconds (μs). The CP length of the first symbol is 5.21 μs, and the length of each of the remaining 6 symbols is 4.69 μs. For an Extended Cyclic Prefix (Extended CP), one time slot contains 6 symbols, the CP length of each of which is 16.67 μs. The uplink/downlink configuration supported is as shown in Table 1:
TABLE 1Downlink-Uplink-uplinkdownlinkswitchingconfigu-pointSubframe numberrationperiod012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUUDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
In Table 1, for each subframe in one radio frame, “D” represents a subframe dedicated to downlink transmission, “U” represents a subframe dedicated to uplink transmission, and “S” represents a special subframe, which contains a Downlink Pilot Time Slot (DwPTS), a Guard Period (GP) and an Uplink Pilot Time Slot (UpPTS).
The TDD supports uplink/downlink switching periods of 5 ms and 10 ms. If the downlink-to-uplink switching point period is 5 ms, the special subframe will be present in the two half frames. If the downlink-to-uplink switching point period is 10 ms, the special subframe is only present in the first half frame. Subframe 0 and subframe 5 as well as the DwPTS are always used for downlink transmission. The UpPTS and the subframe following the special subframe are dedicated to uplink transmission.
The LTE/LTE-A uplink adopts a way of Single Carrier-Frequency Division Multiple Access (SC-FDMA), and a symbol of an uplink time domain is an uplink SC-FDMA symbol.
The Uplink Control Information (UCI) includes a Scheduling Request (SR), Acknowledgement/Negative-Acknowledge (ACK/NACK) response information, and Channel State Information (CSI). The uplink control information may be sent on a Physical Uplink Control Channel (PUCCH), and may also be sent on a Physical Uplink Shared Channel (PUSCH). A PUCCH format supported in the LTE/LTE-A system is described briefly below.
The LTE system supports in total 6 PUCCH formats, which are format 1, format 1a, format 1b, and format 2, format 2a, format 2b respectively. The PUCCH format 1 is used for transmitting the SR, the format 1a/1b is used for transmitting a response signal (ACK/NACK) or for transmitting the response signal and the scheduling request simultaneously, and the PUCCH format 2/2a/2b is used for transmitting the CSI, or the CSI and the ACK/NACK response information. Each PUCCH channel occupies, in one subframe, resources of two physical resource blocks, and occupies, in one time slot, resources of one physical resource block. The PUCCH format 1/1a/1b has the same data-reference signal structure, while the PUCCH format 2/2a/2b also has the same data-reference signal structure.
The most prominent characteristic of the LTE-A system with respect to the LTE system is that carrier aggregation technology is introduced into the LTE-A system, that is, the bandwidth of the LTE system is aggregated to obtain a larger bandwidth. In the system into which the carrier aggregation is introduced, the carrier aggregated is referred to as a Component Carrier (CC), and is also referred to as a serving cell. Meanwhile, concepts for a Primary Component Carrier/Primary Cell (PCC/PCell) and a Secondary Component Carrier/Secondary Cell (SCC/SCell) are also proposed. In the system on which the carrier aggregation is performed, a primary serving cell and a secondary serving cell are at least included, wherein the primary serving cell is always in an activated state.
Since the LTE-A system introduces the carrier aggregation, when the carrier aggregation is adopted, the ACK/NACK response information that User Equipment (UE) needs to feed back will be increased correspondingly. The existing PUCCH formats for the LTE system can only support the feedback of at most 4 bits of ACK/NACK response information. In order to support the feedback of more (exceeding 4 bits) ACK/NACK response information, the LTE-A system introduces a new format, which is referred to as a PUCCH format 3. The channelization process of the PUCCH format 3 is as shown in FIG. 3. The channel structure of the PUCCH format 3 is as shown in FIG. 5. The PUCCH format 3 can support the feedback of at most 20 bits of ACK/NACK response information. Additionally, the PUCCH format 3 has two encoding schemes, for purpose of description, which are referred to as a single Reed-Muller (RM in short) code encoding scheme and a double RM code encoding scheme respectively. When the bits that needs to be fed back are less than or equal to 11 bits, the single RM code will be adopted, whereas when the bits fed back are greater than 11 bits and less than 22 bits, the double RM code will be adopted. The encoding processes in which the single RM code and the double RM code are adopted are as shown in FIG. 4(a) and FIG. 4(b), respectively.
As mentioned previously, the uplink control information that the UE needs to feed back includes 3 parts: an SR, an ACK/NACK response information, and periodic CSI. Since the UE needs to send the SR and the periodic CSI according to a certain period, and at the same time, according to the downlink scheduling, the UE also needs to feed back the ACK/NACK response information. Therefore, on a certain subframe, the UE needs to send multiple kinds of uplink control information simultaneously. When the UE needs to send the ACK/NACK response information and the periodic CSI on the same subframe, there are the following regulations for the existing LTE-A system:
When the ACK/NACK response information that the UE needs to feed back only corresponds to the ACK/NACK response information of the primary serving cell (Pcell), the UE sends the ACK/NACK response information and the periodic CSI by using the PUCCH format 2/2b. In other cases, the UE will discard the periodic CSI and only send the ACK/NACK response information.
The LTE-A system adopts the aforementioned method of multiplexing the uplink control information (the multiplexing here refers to sending two or more kinds of control information simultaneously), because its main goal is to ensure the performance of the downlink throughput. Moreover, in the typical application scenario of the LTE-A (Rel-10 phase), the number of serving cells participating the carrier aggregation is generally 2. Therefore, as long as the periodic CSI of the serving cell is configured appropriately, the probability that the periodic CSI and the ACK/NACK response information are sent on the same subframe may be controlled within a relatively low scope in conjunction with a certain scheduling limit. Thus, the influence on the performance of the system resulting from discarding the periodic CSI is acceptable.
But in the subsequent releases (such as Rel-11) after the Rel-10, the typical application scenario of the carrier aggregation is not limited to 2 serving cells again. With the increase in the number of the serving cells, the probability that the periodic CSI and the ACK/NACK response information collide on the same subframe will increase therewith. If the method of Rel-10 is still adopted, i.e., the periodic CSI is discarded as long as the ACK/NACK response information corresponds to the secondary serving cell, then the accuracy of the CSI obtained on a base station side will decrease, thereby influencing the performance of the downlink throughput.
The existing solution that is not adopted by the LTE-A system is that: the periodic CSI and the ACK/NACK response information are sent simultaneously by using the PUCCH format 3. Specifically, there are the following specific forms:
(1) the periodic CSI and the ACK/NACK response information are encoded in the manner of joint encoding, and the encoded bits are sent by using the PUCCH format 3 after being modulated; and
(2) the periodic CSI and the ACK/NACK response information are subjected to RM encoding and modulation respectively in the encoding way of double RM code, and then sent by using the PUCCH format 3.
However, the above schemes do not consider different error code performance requirements of the ACK/NACK response information and the periodic CSI as well as the importance of the ACK/NACK response information. Thus, when there are more bits of the ACK/NACK response information that needs to be fed back, it is difficult to ensure the performance of the ACK/NACK response information.
Therefore, it is necessary to consider a new scheme for transmitting the ACK/NACK response information and the periodic CSI, which can ensure that the ACK/NACK response information and the periodic CSI are sent simultaneously, and can compromise the detection performance of the ACK/NACK response information and the periodic CSI, thereby ensuring the maximum system throughput and reducing the feedback delay of downlink channel information.